Solder resistant photopolymer composition

ABSTRACT

THIS INVENTION RELATES TO A HEAT AND SOLDER RESISTANT SOLID PHOTOPOLYMER COMPOSITION WHICH CAN BE IMAGED AND DEVELOPED AND A PROCESS OF USING SAME. THE SOLDER RESISTANT PHOTOCURABLE COMPOSITION CONSISTS ESSENTIALLY OF A SOLID DIALLYL PHTHALATE PREPOLYMER, I.E. POLY-(DIALLY ORTHOPHTHALATE) AND A LIQUID POLYENE AND POLYTHIOL. THE SOLID COMPOSITION WHEN APPLIED TO A PRINTED CIRCUIT BOARD AND CURED IMAGEWISE IN THE PRESENCE OF A FREE RADICAL GENERATOR PERMITS PASSAGE OF THE BOARD THROUGH A BATH OF MOLTEN SOLDER TO SECURE ELECTRICAL COMPONENTS, THERETO WHEN THE FREE RADICAL GENERATOR IS ACTINIC RADIATION. E.G., UV LIGHT, A CURING RATE ACCELERATOR, E.G., BENZOPHENON IS USUALLY ADDED TO THE COMPOSITION.

.U.S. Cl. 96115 R United States Patent 3,824,104 SOLDER RESISTANT PHOTOPOLYMER COMPOSITION Harold A. Kloczewski, Pasadena, and William R. Schaefrer, Baltimore, Md., assignors to W. R. Grace &

Co., Washington Research Center, Columbia, Md. No Drawing. Continuation-impart of abandoned application Ser. No. 348,378, Apr. 5, 1973. This application May 24, 1973, Ser. No. 363,453

Int. Cl. G03c 1/70 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to a heat and solder resistant solid photopolymer composition which can be imaged and developed and a process of using same. The solder resistant photocurable composition consists essentially of a solid diallyl phthalate prepolymer, i.e. poly-(diallyl orthophthalate) and a liquid polyene and polythiol. The solid composition when applied to a printed circuit board and cured imagewise in the presence of a free radical generator permits passage of the board through a bath of molten solder to secure electrical components thereto. When the free radical generator is actinic radiation, e.g., UV light, a curing rate accelerator, e.g., benzophenone "is usually added to the composition.

This application is a continuation-in-part of copending application having Ser. No. 348,378, filed Apr. 5, 197 3, now abandoned.

This invention relates to a solid solder resistant photopolymer composition and a process which permits soldering of electrical or electronic components to printed circuit boards in a molten solder bath.

The soldering of electrical components to a printed circuit board is a multi-step, time-consuming task. More precisely, before the electrical components can be soldered to the board, the following steps must be carried out. An insulating board such as epoxy Fiberglas board must be copper-clad. The copper-clad board is then drilled through at predetermined sites. The boards are then debnrred and cleaned and the cladding is washed in ammonium persulfate solution and then in water, 5-10% H250 solution or other solvent to remove excess ammonium persulfate. A catalyst is then applied to the board for electroless deposition of copper to coat not only the inside of the drilled holes, but also the entire board. Following electroless deposition of copper, additional copper is put on the board and in the holes by electroplating. The thus electroplated copper is then covered with a conventional photoresist and exposed imagewise through a printed circuit transparency to UV light, thus curing (hardening) the exposed portion of the photoresist. The unexposed portion of the photoresist is washed ofl, exposing the copper thereunder, i.e., where the lands, wiring conductors and connecting pads are formed. Positive working resists can also be used, if desired at this stage. The thus exposed copper circuit is then electroplated in a tin-lead plating bath, thereby coating solder onto the exposed copper on the board and in the holes. The cured photoresist is then stripped in a solvent and/ or by mechanical means and the copper under the cured photoresist is etched away in a conventional copper etching bath. It is at this point that one can then commence the sequence of steps necessary to solder electrical components to the circuit board.

Present day technique employed for soldering electrical components to a circuit board are being made obsolete by space limitations. The trend toward smaller and more functional computer systems is shrinking. the size ice of the boards, making the lines and pads smaller and closer together. In addition, the increased functionality is requiring more multilayers for connections. Diminished size also means shorter distances between components and therefore faster speed of computer operation. Manufacturers presently solder by passing the board, coated with a heat cured screen printed solder resistant ink, through a wave soldering machine to allow the thousands of connections to be made quickly. However, the limitations on screen printing are already apparent on large 24" x 20") multilayer computer platters. The next generation of computers will require line spacings which are totally beyond screen printing; therefore, a need for a solder resistant photoresist exist. To overcome the drawbacks of solder resist inks, liquids photosensitive materials have been added to the art. However liquid photosensitive compositions have the drawback that on boards which have to be processed on both sides, one must carry out the sequence of applying the composition to the board, exposing imagewise and developing on one side of the board before the board can be turned over to repeat the operation. A solid solder resist permits double side application, exposure and development simultaneously.

One object of the instant invention is to produce a solid solder resistant composition. Another object of the invention is to produce a photocurable solder resistant composition which can be applied and photocured, imagewise, in register with suflicient accuracy to meet the requirements of the next generation of printed circuit boards. Still another object of the instant invention is to produce a photocurable solder resistant composition which, in its cured state, is capable of withstanding molten soldering bath temperatures in the range of 400- 600" F. A still further object of this invention is to produce a process employing the solder resistant photopolymer compositions which can be applied with sufiicient accuracy to meet the next generation of printed circuit boards. Yet another object of this invention is to produce a process whereby the solid solder resist on both sides of the printed circuit board can be applied, exposed and developed simultaneously.

The critical ingredients in the solder resistant photopolymer composition are:

(1) 5 to 40 parts by weight of a polythiol containing at least two thiol groups per molecule;

(2) 60-95 parts by weight of poly-(diallyl orthophthalate), the sum of (1) and (2) being parts by weight;

(3) 1 to 20 parts by weight based on the weight of (l) and (2) of a liquid polyene of the formula:

omoornon=orh 0 CH2- C 2H5 nzocnion=om and l (4) 0.05 to 10 parts by weight based on the Weight of (1) and (2) of a photocuring rate accelerator.

It is to be understood, however, that when energy sources other than visible or ultraviolet light are used, to initiate the curing reaction, i.e. high energy ionizing radiation, photocuring rate accelerators (i.e., photosensitizers, etc.) generally are not required in the formulation. That is to say, the actual composition of the photo curing rate accelerator, if required at all, varies with the type of energy s'ou rce' that'isused to initiate the curing curable solder resistant photoresist. That is, without the solid poly-(diallyl orthophthalate) and the polythiol being presentyno photocurable solder resist results. Furthermore the-solid poly-(diallyl orthophthalate) being present in .a major amount insures that the photocurable composition is a solid even though minor amounts of liquid polyene and polythiol are added to the composition. This allows the image bearing negative to be placed in direct contact with the Mylar substrate thus affording higher resolution on exposure and also allows simultaneous application, exposure and development on both sides of the printed circuit board.

The liquid polyene operable in the instant invention is set out supra. The function of the liquid polyene is two fold. It not only takes part in the crosslinking reaction with the polythiol but also, more importantly, affords sufficient adhesiveness to the composition to allow it to operate as a solder resist. That is, absent the liquid polyene from the composition, the cured composition on passing through the heated solder bath bubbles up and separates from the board as will be shown in an example hereinafter.

The amount of the liquid polyene added to the formulation is critical. That is if amounts in excess of the upper limit set out herein are added, then the material no longer is a solid and thus precludes simultaneous application, exposure and development on both sides of the board. If an amount less than the lower limit of the liquid polyene is added then insufiicient adhesion is obtained and the photoresist bubbles up and fails to adhere to the board.

Various photosensitizers, i.e. photocuring rate accelerators are operable and well known to those skilled in the art. Examples of photosensitizers include, but are not limited to benzophenone, acetophenone, acenapthenequinone, methyl ethyl ketone, valerophenone, hexanophenone, 'yphenylbutyrophenone, pmorpholinopropionphenone, dibenzosuberone, 4-morpholinobenzophenone, 4-morpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetophenone, benzaldehyde, a-tetralone, 9-acetylphenantherene, 2-acetylphenanthrene, -thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, 9-fiuorenone, l-indanone, 1,3,5-triacetylbenzene, thioxanthen-9- one, xanthene-9-one, 7-H-benz[de]anthracen-7-one, 1- naphthaldehyde, 4,4'-bis dimethylamino benzophenone, fluorene-9-one, 1-acetonaphthone, 2-acetonaphthone and 2,3-butanedione, etc., which serve to give greatly reduced exposure times and thereby when used in conjunction with various forms of energetic radiation yield very rapid, commercially practical time cycles by the practice of the instant invention.

As used herein, the term polythiols refers to simple or complex organic compounds having a multiplicity of pendant or terminally positioned SHfunctional groups per average molecule.

On the average the polythiols must contain 2 or more -SH groups/molecule. They usually have a viscosity range of 0 to 20 million centipoises (cps) at 70 C. as measured by a Brookfield Viscometer. Included in the term polythiols as used herein are those materials which in the presence of an inert solvent, aqueous dispersion or plasticizer fall within the viscosity range set out above at 70 C. Operable polythiols in the instant invention usually have molecular weights in the range 5020,000, preferably The polythiols operable in the instant invention can be exemplified by the general formula:

where n is at least 2 and R is a polyvalent organic moiety free from reactive carbon to carbonuns'aturation: "Thus R may contain cyclic groupings and minor amounts of hetero atoms such as N, S, P or 0 but primarily contains carbon-hydrogen, carbon oxygen, or silicon-oxygen containing chain linkages free of-any reactive carbon to carbon unsaturation. i

. One class of polythiols""operable with polyenesin the instant invention to obtain a polythioether solder resist are esters of thiol-containing acids of the general formula: HSR "COQH where R is an organic moiety containvin g no reactive carbon to carbon unsaturationgwith polyhydroxy compounds of the general structure:

where R is an organic moiety containing no reactive carbon to carbon unsaturation and n is 2 or greater. These components will react under suitable conditions to give a polythiol having the general structure where R and R are organic moieties containing no reactive carbon to carbon unsaturation and n is 2 .or greater.

Certain polythiols such as the aliphatic monomeric polythiols (ethane dithiol, hexamethylene dithiol, decamethylene dithiol, tolylene-2,4-dithiol, etc.) and some polymeric polythiols such as thiol-terminated ethylcyclohexyl dimercaptan polymer, etc. and similar polythiols which are conveniently and ordinarily synthesized on a commercial basis, although having obnoxious odors, are operable in this invention but many of the end products are not widely accepted from a practical, commercial point of view. Examples of the polythiol compounds preferred for this invention because of their relatively low odor level include, but are not limited to, esters of thioglycolic acid (HS-CH COOH), u-mercaptopropionic acid (HSCH CH )COOH) and fi-mercaptopropionic acid (HSCH COOH) with polyhydroxy compounds such as glycols, triols, tetraols, pentaols, hexaols, etc. Specific examples of the preferred polythiols include, but are not limited to, ethylene glycol bis (thioglycolate), ethylene glycol bis (fi-mercaptopropionate), trimethylolpropane tris (thioglycolate, trimethylolpropane tris (p-mercaptopropionate), pentaerythritol tetrakis (thioglycolate), tris (hydroxyethyl) isocyanurate tris (B-mercaptopropionate) and pentaerythritol tetrakis (fi-mercaptopropionate), most of which are commercially available. A specific example of a preferred polymeric polythiol is polypropylene ether glycol bis (B-mercaptopropionate) which is prepared from polypropylene ether glycol (e.g., Pluracol P2010, Wyandotte Chemical Corp.) and fl-mercaptopropionic acid by esterification.

The preferred polythiol compounds are characterized by a low level of mercaptan-like odor initially, and after reaction, give essentially odorless polythioether end prod ucts which are commercially attractive.

The term functionality as used herein refers to the average number of ene or thiol groups per. molecule in the solid or liquid polyene or polythiol, respectively. For example, a tetraene is a polyene with an average of four reactive carbon to carbon unsaturated groups per molecule and this has a functionality (f) of four. A dithiol is a polythiol with an average of two thiol groups per molecule and thus'has a functionality (f) of two.

To obtain the maximum strength, solvent resistance, creep resistance, heat resistance and freedom from tackiness, the reactive components consisting of polyenes and polythiol in combination with the curing rate accelerator of this invention are formulated in such a manner as to give solid, crosslinked, three dimensional network polythioether polymer systems on curing. In

ordergt'o "achieve such infinite network formation, the individual polyenes and polythiol must each have a functionality of at least '2 and the sum of the functionalities of the" polyene and polythiol components must always be greater than 4.-

The solid solder resistant photopolymer compositions tobe cured, in accord with the present invention may, if "desiredyinclude such additives as stabilizers, antioxidants, accelerators, dyes, inhibitors, activators, fillers, pigments, anti-static agents, flame-retardant agents, surface-active agents, extending oils, plasticizers, and the like within the scope of this invention. Such additives are usually preblended with the polyene or polythiol prior to or during the compounding step. The aforesaid additives may be present in quantities up to 500 or more parts based on 100 parts by weight of the polyene/polythiol solder resist compositions and preferably 0.005- 300 partsonithe same ,basis.

To insure that the reaction does not precure prior to use, stabilizers are usually added to the polyene prior to admixture with the polythiol. Operable stabilizers include various -well known commercially available materials such as octadecyl p-(4-hydroxy-3,S-di-t-butylphenyl) propionatecommercially .--.available .from Geigy Chemical, (10., under the trade name Irganox 1076; 2,6-ditertiarybutyl-4-methylphenol commercially available under the trade name Ionol from --Shell Chemical Co., pyrogallol, phosphorous acid, hydroquinone and the like. The stabilizers are usually added in amounts ranging from 0.01 to 5 .0 parts. per 100 parts by weight of the poly- ;(di'allyl orthophthal'ate) /polythiol composition. """To'facilitatehandling and application the solid solder resistant photocurable.composition is cast in a solvent on a UV transparent film substrate, dried and covered with a protective plastic ,coversheet, e.g. polyethylene which can be then rolled up. The poly-(diallyl orthophthalate), polythiol and liquid polyene along with a curing rate accelerator, dye and any"stabilizers desired are mixed in an equal weight of a sol-vent for these materials. Ethylene dichloride is an operable solvent for the solder resist materials, however other well known solvents in eluding'but hot limited.to methylene chloride, chloroform, 1,l, 1'-trichloroethane, mono, o-di and trichlorobenzene and the like, are operable. The reactants can be added to the solvent in any order but preferably the polyen'es both: liquid and solid"are added first followed by stabilizers therefor with the remainder of the materials being added thereafter. The admixing is carried out at room temperature although slightly, elevated temperatures can be employed if desiredu After' the solution is homogeneous i 'scoated onto a UV transparent substrate,

Mylar. The li lyl'afi'is"placed ona tempered glass plate which is heated to 7080 C. and the material is applied by. ,a, calibrated..draw bar drawn across the surface to apply al6 "mil thick "coating. Thewet coating is then dried :for 1. to .B hours, at 70.;-80C. resulting in an approximately .8 mil thick photocurable solder resist composition on the .Mylar substrate.After drying the coated substrate is covered witha protective polyethylene film (2 mil thick), rolled up on a take-up roll and is ready forusep. a

The preferredmeans of: curing: is by means, of'electromagnetic radiation of wavelength of about 20004000 A. (because of simplicity, economy and convenience). The polyene-polythiol solder resistant composition of the instant invention can be cured also by image wis e directed beams of ionizing irradiation. 1

When UV radiation is used for the curing reaction, an intensity of 0.004 to 6.0 watts/em. is usually employed;

Unless otherwise noted herein, all parts and percentages are by weig ht. The following examples will explain but expresslyhot limit the instant invention.

thick film of polyethylene terephthalate, i.e.

6 EXAMPLE I Preparation of Liquid Polyene A round bottom flask is fitted with a stirrer, thermometer, dropping funnel, nitrogen inlet and outlet. The flask can be placed in a heating mantle or immersed in a water bath as required.

Two moles (428 gms.) of trimethylol-propane diallyl ether were mixed with 0.2 cc. of dibutyl tin dilaurate under nitrogen. One mole of toly1ene-2,4-diisocyanate was added to the mixture, using the rate of addition and cooling water to keep the temperature under 70 C. The mantle was used to keep the temperautre at 70 C. for another hour. Isocyanate analysis showed the reaction to be essentially complete at this time resulting in the following viscous liquid polyene product:

i oH.=oHoH.-0om o o H5C2CCH2O(I.L-NH NHPJ- cm: 0 nom- 0 cm on. 0 on. onion,

0 CH2 C2135 CH OCH CH=CH which will be referred to hereinafter as Prepolymer A.

EXAMPLE II 10 parts by weight of the liquid polyene from Example I (Prepolymer A), parts by weight of commercially available poly-(diallyl orthophthalate) and as stabilizers, 0.2 parts by weight of phosphorous acid, 0.044 parts hydroquinone, and 0.015 parts pyragallol were admixed with 20 parts by weight of pentaerythritol tetrakis (B-mercapto-propionate) commercially available from Carlisle Chemical Co. under the trade name of Q-43, 0.1 part by weight of sudan green dye and 8.0 parts by weight benzophenone in parts by weight of ethylene dichloride. The mixture was stirred at room temperature for /2 hour at which time all ingredients were in solution. The photocurable solution was then coated onto a .1 mil thick Mylar film extended on a tempered glass plate which was heated to 76 C. A calibrated draw bar set so as to coat a 16 mil thick coating was drawn across the photocurable composition. After drying for 75 minutes at 76 C., an 8 mil thick. film of the dried solid photocurable composition resulted. The dried coating was covered with a 2 mil thick polyethylene protective cover sheet and the laminate was rolled up on two takeup rolls. The rolls were placed in a Du Pont Laminating Machine, the polyethylene cover sheets removed and the coated Mylar substrates were laminated to both sides of a drilled printed circuit board (coated surface being laminated to the board) at a temperature of 160 F. and a speed of 4 feet per minute. The board prior to coating had been electroless plated and electrolytically plated with copper followed by an electrolytic plating of tinlead over the etched copper circuit thereon on both sides of the board. The photocurable composition on both sides of the board was exposed through a transparency imaged in the pad areas and in contact with the Mylar substrate, to a 275 watt Westinghouse U.V. sunlamp at a surface intensity on the composition of 4,000 microwatts/cm. for 7 minutes. The major spectral lines of the sunlamp were all above 3000 angstroms. The Mylar substrate was then stripped ofl? both sides of the board leaving the composition on the board and the images on he board surfaces were developed by spraying with O-dichlorobenzene for 4 minutes. The resulting reso lution was excellent. The board was then washed with water for 1 minute and air dried at 75 C. forlS minutes. The dried board was then baked in an air oven at C. for 35 minutes.

The leads of electrical components were inserted through the holes in the board. Using a standard commercially available solder machine, the board was then passed over foaming flux, i.e. Reliavos 346-35, a fast drying activated rosin flux, commercially available from Alphametals Inc., Jersey City, NJ., to coat the pad areas to be soldered with the flux. The board was then conveyed over a preheater maintained at a temperature sufficient to raise the temperature of the circuit board to the range 210-225 F. and then over a solder bath maintained at 500 F. The solder is then splashed on the under side of the board, thereby soldering the leads extending there through to the board. The printed circuit boards with the electrical components soldered thereto are then washed in 1,1,1-trichloroethane to remove the flux and then dried. Inspection of the board showed that the cured composition was unaffected by the soldering steps and adhered well to the board.

EXAMPLE III Example II was repeated except that the 10 parts by weight of the liquid tetraene from Example I (Prepolymer A) was omitted from the formulation.

Inspection of the board after passing through the solder bath showed that the solder resist coating was bubbled up over the entire board due to its poor adhesion.

EXAMPLE IV 47 parts by weight of the liquid tetraene from Example I (Prepolymer A) containing as stabilizers 0.2 parts by weight phosphorous acid, 0.044 parts hydroquinone and 0.015 parts pyragallol were admixed with 38 parts by weight of pentaerythritol tetrakis (B-mercaptopropionate), 0.1 parts by weight of sudan green dye and 8 parts by weight benzophenone. The admixture was heated to 60 C. to dissolve the stabilizers in the tetraene. The viscous liquid admixture was coated onto the entire surface of one side of a drilled printed circuit board to a thickness of 8 mills by means of a calibrated draw bar. The board prior to coating had been electroless plated and electrolytically plated with copper followed by an electrolytic plating of tin lead over the etched copper circuit thereon on both sides of the board. The photocurable composition was exposed through a transparency imaged in the pad areas (with an air gap of 8 mils between the liquid composition and the transparency) to a 275 watt Westinghouse =UV sunlamp at a surface intensity on the photocurable composition of 4000 microwatts/cm. for 1 minute. The major spectral lines of the sunlamp were all above 3000 angstroms. Such exposure caused curing and solidification of the exposed photocurable solder resist composition. The unexposed photocurable composition was removed by washing in an aqueous detergent solution containing sodium metasilicate and polyoxyethylene tridecyl ether. The coating, imaging and development steps were repeated on the other side of the board. Inspection of the board at this point showed poor resolution due to the necessity of maintaining an air gap between the image transparency and the liquid photocurable composition. Additionally it was noted that the liquid photocurable composition had entered some of-the holes in the board and cured therein thus necessitating its removal prior to inserting electrical components in the holes. If the cured material is not removed from the holes completely, poor soldering joints results. Leads of electrical components were inserted through the holes in the board. Using a standard commercially available solder machine, the board was passed over foaming flux, i.e. .Reliavos 346-35, a fast drying activated rosin flux: w commercially available from Alphametals, Inc., Jersey City,'N.J., to-coat the pad areas to be soldered. The board was then conveyed over a preheater maintained at a temperature of 700 F. and then over a solder bath maintained at a temperature sufficient to raise the temperature of the circuit board to the range 210225 F. The solder splashing on the underside .ofthe board.

soldered the leads extending therethrough to the-board; The board was then washed in waterto remove theiflux and then dried. Althoughadhesion of; the solder-resist to,-

the board appeared good it should be noted thatrsincej the photocurable solder resist is a-;liquid composition, it was necessary, to.coat,qexpose;and .develop oneside, of the board prior to carryingout these steps on the other side of the board-thus necessitatinga doubling-of the time cycle as compared to a solid solder resist.

In practicing the instant invention-the photocurable solder resist is usually applied soias to obtain adriedsolid layer having a thickness in the range 4 to 10 mils.

EXAMPLEY Example 11 was repeated except that the photocurable solder resist composition was as follows; v.

2.6 parts by weight of the liquid polyene from'Example'I (Prepolymer A); g parts by weight of commercially available' poly-(diallyl' orthophthalate); I r

10 parts by weight pent'aerythritol tetrakis' (B-mercapto propionate; Y 1

0.1 part by weight of s'uda'n green dye'and' {7 .4 partsby weight benzophenone in 100 parts by weight of'ethylene dichloride; i g 1 0.044 parts by weight hydroquinone;

0.015 parts by weight pyrogallol;

0.2 parts by weight phosphorous acid.

Inspection of the board showed that the cured composi tion was unalfected by the soldering step, and adhered well to the board.

EXAMPLE VI Example II was repeated except that the photocurable solder resist composition was as follows:

1.0 part by weight of the liquid polyene from Example I Inspection of the board showed that the. cured composi tion was unaffected by the soldering step and adhered well to the board. Y v

What is claimed is: v

1. A solid photocurable solder "resist "com'positio'ncon sisting essentially of: V p i H (l) 5 to 40 parts by; weight ofa polythiol containing at least two thiol groups per molecule; (2) 60 to parts b'y'we'i'ght Ofpoly-(diallyhorthophthalate), the sum 05(1) and (2 being parts by weight; (3) 1 to 20 parts by weight based on the weight "of (1') and (2) of a liquid polyeneof the-formulafi 9 10 and 3,475,176 10/1969 Rauner 96-115 R (4) 0.05 to 10 parts by weight based on the weight of 3,721,723 3/1973 Heidel et a1. 204-1595 (1) and (2) of a photocuring rate accelerator. 3,619,393 11/1971 Stahly 204-159.15 3,701,721 10/1972 Lard 204159.16 References (Med 5 3,708,413 1/1973 Kehr et a1. 204-15914 UNITEDSTATES PATENTS RON D H. H, 3,753,720 8/1973 Kloczewski et a1. 96-115R AL SMIT Puma Bummer 3,615,450 10/1971 Werber et a1. 96--35.1 KIMLIN, AssistantExaminer 3,767,398 10/1973 Morgan 9636.2 3,770,491 11/1973 Spoor et al. 204-15915 3,462,267 8/1969 Giangualano et a1. 96-35.1 96-35.1, 115 P; 204159.13, 159.14, 159.15 3,376,139 4/1968 Giangualano et a1. 96-35.1 

